Direct current restorer for maintaining constant black level at cathode-ray tube



w. F. BAILEY 2,611,029 DIRECT CURRENT REsToRER FCR MAINTAININC CONSTANT Sept. 16, 1952 BLACK LEVEL AT CATHODE-RAY TUBE Filed Jan. 2l, 1950 m m a MvNBw- 2 "m 2 I ATTO R NEY Patented Sept. 16, 1952 UNITED srrss William F. Bailey, Valley Stream,N. Y., assignor TENT OFFICE l to Hazeltine Research, inc., Chicago, Ill., a corporation of Illinois Application January 21, 1950, Serial No. 139,935

GeneralY The present invention relates to television receiver signal-translating systems and is particularly directed to the improvement of the con- 5 tic. This operating requirement is necessary in trast-brightness characteristic of such systems. order that signal components representing lany Such systems have special application to a teleother given shade value at all times appear with vision receiver intended to utilize a negatively the proper value in the reproduced image; Also, modulated carrier-wave television signal and will where the receiver utilizes alternating-current be set forth in that environment. coupling arrangements between stages, signal In present-day practice, the composite tele- Stabilization is vrequired in order to ensure that vision signal transmitted to a receiver comprises the background illumination component is presa carrier-wave signal modulated during recurentin the signal applied to the reproducing derent trace periods with video-frequency and lowvice. frequency or direct-current components, repre- Furthermore, the eye oi an observer is respon-4 senting light variations in an image being transsive primarily to the contrast or ratio betweenl mitted and its average background illumination illumination values rather than the absolute value respectively. During intervening retrace periods oi any given shade of illumination. Therefore, the carrier signal is modulated with synchronizit is desirable to provide an arrangement for ading-signal components. Where negative modu- 2o justing the extreme values of illumination in theV lation is employed, a certain amplitude range of reproduced image. Such an adjustment is re the carrier-wave signal, or up to 75% of the maxferred to as a contrast control and permits adimum carrier amplitude, is devoted to the transjustment of the receiver in accordance with conmission of the video information. The lower ditions of receptOIl and the type 0f Picture belimit of the modulation range used to transmit ing received. video components designates the white level, its in conventional receivers of one type, signal upper limit corresponds to the black level, and a stabilization is obtained through a diode circuit decrease in carrier-wave amplitude within the which peak recties the synchronizing comrange denotes an increase in illumination. The ponents of the detected signal, stabilizing this final portion of the carrier amplitude, from 75 3o signal with respect to its synchronizing peaks. to 100%, is assigned to the transmission of the Additionally, a gain control is frequently insynchronizing signals including line-frequency eludedV in one of thevideo-amplier stages for components whichintervene succeeding lineeffecting contrast regulation. Such an arrangetrace periods and held-frequency components ment does effect stabilization but does not precoming between successive eld-trace periods. serve the contrast-brightness characteristic of the Each synchronizing component extends from the receiver as uniform as may be desired in certain black level of the video signal a fixed amount into installations. This is because the black level of a the blacker-than-black region. vAt the receiver, negatively modulatedsgnal is al? an amplitude the described composite signal is detected and its that is appreciably less than the peak amplitude video-modulation components are utilized to modrepleSSYlted by the SyIlChlOIlZIlg-Sgnl 00mvu late the intensity of the bea-m of a cathode-ray type reproducing device The synchronizing components of signal control scanning apparatus An important requirement in a properlyoperating receiver is accurate stabilization ofthe detected signal with respect to a well-#donned signal level, such as the black level or some other predetermines shade level. stabilization of this type-is necessary to facilitate adjusting the reproducing 5 Claims. (Cl. INS-7.5)

device so that a given signal level or amplitude corresponding to black or some other predetermined shade level is effectively held fixed with respect to its signal input brightness characterisponents. Therefore, as the incoming signal intensity varies, the black level tends to deviate considerably with reference to the stabilization level. Accordingly, with such receivers a very accurate gain-control arrangement is required, or adjustment of the brightness control is necessary with variations in signal intensity, if theblaok level is to be held fixed with respect to the signal input brightness characteristic of the reproducing device.

In another receiver described in a copending application of Arthur V. Loughren, Serial No. 643,288, filed January 25, 1946, entitled Television Signal-Translating System, contrast control and black-level stabilization is obtained by means of a circuit arrangement which includes in one portion thereof two signal-translating channels. The signals in one of these channels are proportioned to have an amplitude relationship of the order of three to one to those in the other channel. A signal is derived in the other of the channels which is equal in magnitude to but opposite in polarity to the predetermined shade level or black-level signal translated through the one of the channels. A voltage-divider circuit is provided for combining the signals present in these channels to produce a resultant video signal having a black level which is stabilized with respect to variations in the average amplitude of the video signal. Though this type of arrangement is an improvement over the type of arrangement used in conventional receivers and provides aresultant video signal that has a stable black level Athat does not vary as the incoming signal intensity varies, it is sometimes desirable to obtain more signal gain or an output signal l.of .greater intensityT than that obtained from the system Ajust described. when using substantially the same number of amplification stages.

It is an object of the present invention, therefore, to provide a new and improved television signal-translating system which avoids one` or more of the above-mentioned limitations of prior arrangements.

It is another object of the invention to provide a new and improved television .signal-translating system having an improved contrast-brightness characteristic.

It is a specic object of the invention to provide a new and improved television signal-translating system having an improved black-level signal stabilization arrangement wherein more than one video-frequency amplifier stage .may be employed.

In accordance with the invention, a television receiver signal-translating system for translating a video-frequency signal having one amplitude level representative of synchronizing-signal peaks while a predetermined fractional portion of that level is representative of black comprises a source of unidirectional potentials, one thereof being positive with respect to a predetermined reference level and another thereof being effectively negative with respect to this reference level. The system includes a first video-frequeni cy amplifier for translating the video-frequency signal, comprising an electron-discharge device having a plurality of electrodes including an anode, and comprising a potential-isolating impedance coupled between the anode and the positive potential source. The system also includes a potential-divider network including an intermediate terminal and including a pair of terminals one of which is coupled to the anode and the other to the negative potential source, the portion of the network coupled between the negative potential source and the intermediate terminal having an impedance-with relation to the total impedance of the network as is the amplitude of the synchronizing signal to the overall amplitude of the video-frequency signal. The system additionally includes a second video-frequency amplifier including an input circuit having at least two signal-translating channels, one thereof being capacitively coupled to the anode o f the first amplier lfor translating the videofrequency signal developed across the network, and the other of these channels being conductively connected to the intermediate terminal for translating the signal developed in the aforemen- 4 tioned portion of the network and providing a unidirectional potental for the input circuit. Finally, the system includes a signal-stabilizing network comprising a peak-rectifying circuit including a unidirectionally conductive device coupled between the channels and so poled as to conduct upon the application of the peaks of the synchronizing signals thereto and to combine the signals translated in each of the channels, thereby to produce in the aforementioned input circuit a resultant video-frequency signal having a -level representative of the aforementioned black level and stabilized so that the last-mentioned black level is substantially independent of variations in the average amplitude of the firstmentioned video-frequency signal.

For a Abetter understanding of the present invention, together with other and further objects thereof, ireference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. A1 is a circuit diagram, partly schematic, of a complete television carrier-signal receiver embodying the television signal-translating system of the present invention in a particular form; and Figs. Zar-2d, inclusive, comprise graphs useful in explaining the operation ofthe invention.

Description of television receiver of Fig. 1

Referring now more particularly to Fig. l, the television carrier-signal receiver there represented includes aradio-frequency amplifier I0 of any desired number of stages, having its input circuit connected to an antenna system II, I2 and having its output circuit connected to an oscillator-modulator I3. Coupled in cascade with oscillator-modulator I3, in the order named, are an intermediate-frequency amplifier I4 of one or more stages, a detector and automaticgain-control or A. G. C. supply I5, a signal-translating system I6 including a video-frequency amplifier and an image-reproducing device I1 of the cathode-ray tube type. Unit I6 is described more particularly hereinafter. There is also coupled to detector I5 a synchronizing-signal separator I8, having output circuits connected to a linescanning generator I9 and a field-scanning generator 20. The output circuits of these scanning generators, in turn, are connected to appropriate beam-deecting windings 38, 39 of device I'I. The output circuit of the A. G. C. supply included in the detector I5 is connected to the input circuits in one or more of the tubes of radio-frequency amplifier lI 0, oscillator-modulator I3, and intermediate-frequency amplier I4 in a conventional manner.

A sound-signal reproducing unit 2| is also connected to the output circuit of oscillator-modulator I3. It may include one or more stages of intermediate-frequency amplification, a detector,

one or more stages of audio amplification, and a sound-reproducing device.

Description of operation of television receiver of Fig. 1

It will be understood that the various units thus far described, with the exception of signaltranslating system I6, may be of conventional construction and operation. The details of such components are well known in the art rendering a further description thereof unnecessary. Considering briey the operation of the receiver as a whole, and neglecting for the moment the specific operation of unit ,I 6a desired modulated carrier-wave television signal is intercepted by .antennav system II', I2. This signal is selected and amplied in radio-frequency ampliiier Illvand applied to oscillator-modulatorV I3 where it is converted to an intermediate-frequency signal. The intermediate-frequency signal is selectively amplied in amplifier I4 and is detected by detector I5 to derive the modulation components thereof. These modulation components, which comprise synchronizing components, video-frequency components and direct-current` -components, are applied to the video-frequency ampliiiers of unit I6 for amplification and are thereafter applied to thebrilliancy-control elec- Itrode of image-reproducing unit Il to modulate the intensity of the electron beam thereof in accordance with the video-frequency components The synchronizing-signal components of the received signal are separated from the video-frequency components in synchronizing-signal separator I8 and are used to synchronize the operation of the line-scanning and field-scanning generators I9 and 20, respectively. These generators produce scanning signals of saw-tooth wave form which are properly synchronized with` reference to the received signal and are applied to the defiecting elements 38, 39 of the image-reproducing unit, thereby to deflect the cathode-ray beam of the cathode-ray tube of unit Il in two directions normal to each other to reproduce the received television image. l f

The automatic-gain-controlror A. G.'C. signal derived in unit I5 is effective to control the amplification of one or more of units I9, I3 and I4 to maintain the signal input to `detector l 5 within a relatively narrow range for a wide range of re ceived signal intensities. y

The sound-signal modulated carrier wave accompanying the video-signal modulated carrier wave is also intercepted by antenna system II, I2.'

It is selected and amplied in radio-frequency A amplifier I0 and applied to oscillator-modulator i3 where it is vconverted to a soun-d modulated intermediate-frequency signal. The sound modulated intermediate-frequency signal is applied to unit2I' wherein it is ampliiied and detected to derive the modulation components which are further amplified and reproduced by the ysoundreproducing device. y Y

Description of signal-translating system 0f Fig. 1

Idivider 31 connected therebetween and, having a grounded intermediate point providing a predetermined reference level. l

The unit I6 also has a iirst repeater for translating a video signal applied thereto, having an output circuit including an impedance network, part of which is supplied from the source of potentials with a potential of one polarity and another part thereof being supplied from the same source with a potential eiectively of opposite polarity. This iirst repeater comprises a videofrequency amplier stage including an electrondischarge tube 22 conductively coupled to the output circuit of the detector I5. The tube 22, which may comprise a pentode, includes, among others, an anode, a cathode and a control electrode, the cathode thereof being connected through a bias resistor 23 to ground. The tube 22 also has an output circuit including the anode load circuit thereof comprising an impedance or resistor network of series-connected resistors 24, 25 and 26, having parts thereof supplied with voltages of opposite polarity. 1n particular, potential +B is supplied through resistor 2t to the anode of tube 22, while resistors 25 and 25 are coupled between the anode and the source of potential -B. f

The impedance network 22, 25 and 26 has first and second portions so proportioned that the amplitude of the signal developed in the first portion is a predetermined fraction of the amplitude of the signal developed in the second pori tion. The resistor` 26 comprises the first portion of the network while the resistors 25 and 25 comprise the second portion thereof, the proportioning of the resistors 25 and 26 being such that one-fourth of the amplitude of a signal developed across lthe resistors 25 and 26 is developed across the resistor 26.

The unit I B also comprises a second repeater having an input circuit including at least two signal-translating channels, one of these channels being coupled to the rst portion of the described impedance network for translating the signals developed in this network and for providing a unidirectional bias potential for the input circuit, and the other of these channels being coupled to the second portion of that network for translating the signals developed therein. The second repeater comprises an electron-discharge tube 2l, which may comprise a pentode, having, among others, an anode, a cathode and a control electrode. The control electrode of the tube 2l is conductively connected through one oi the channels comprising a resistor 23 and a conductive lead 29 to the junction of the resistors 25 and 26, thereby providing a channel which is coupled to the rst portion 25 of the network '22, 25, 26 for translating the signals developed therein and for providing a unidirectional bias potential for the control electrode of the tube 2l. The control electrode of thevtube 2l is also connected through another channel comprising a condenser 3U to the junction of the resistors 2t, 25 and to the .anode of the tube 22, thereby being couple-:l to the second portion 25, V26 of the resist/or network 24, 25, 26 for translating signals developed therein. The tube 21 also has an anode load resistor 3| and a cathode load resistor 32.

Unit I6 also comprises a stabilizing circuit for combining the signals translated in each of thev described channels to produce in the input ciri cuit of the tube 2l a resultant video signal having a shade level related to the predetermined shade level and for so stabilizing the resultant signal that the last-mentioned shade level is substantially independent of variations of the average amplitude of the first-mentioned video signal. This stabilizing circuit includes a diode rectifier 33 having the condenser 3i) in the anode circuit thereof and the resistor 28 coupled between the anode and cathode thereof, thereby effectively being coupled across the resistor 25 and between the two signal-translating channels.

Unit I6 also includes output terminals t and 3 5 -for-fcouplingethefv amplifier -fl 6 ltof-the :image-reproducingr'unit I 1.'

Operation. of siguatranslting, system of l'g.V 1.

Considering-'nowtheoperation .of the television 1 receiver signal-translatingzfsystem just described; thevideo signal which is detectediinunit,I5-.1s

directly applied .toxthefcontrol .electrode of v. video`.-

frequency amplier'. 22 l and.: is.` amplified'. by the'V latter: Anampliedwideofsignal therefore de: veloped'. across; the; resistor: network.. 24, 25. and 26:. Resistor 2.4 'effectively actsasz part of theload resistor betweemthe anoderof :tub'e .'22 and. the;V

sourcemf -i-B: pOtentiaLbattery- 36;. andjs eiec.-

tively connectedjn .parallel withi the other. load..

resistors 25 and 26 through the voltage dividerl toground. The .-rst ;portion;of thel resistor .network comprising the'fresistor 2 6 develops asignal voltage,- the amplitude; of fwhich; is :proportioned to beeoneffourtn that; of I. the; amplitude f of; the, signal developed.acrossresistors,25randg25f The: video. signal, developed..acrossgresistors :2E-Land. 26" is applied through.theisignalftranslating channel.V including, condensers 30 in aconventional l man-- ner, Vto the anode ;of diode rectier: 33.y

The relative. amplitudesgof; the components of.. the; video signals present .on...theA anode;;.of .tube-- 22 as functions of the carrier-wavezsignallevelor.

intermediate-frequency signal level. are representedby theseries.of.curves.in Fig, 2a. In .this figurefand the gseries.A of curves.- to .beL describedhereinafter in .connection .with Figs;` 2li-2d, S1 deseA ignatesthefvariation inamplitude.A of .the recur.-A Y

rent .org synchronizingfsignal components, Bf. the

reference level or from.the.-Whitexsignal `level under ideal operating. conditions. The black level, represented by curveB, has van amplitude Which corresponds to a signal intensityintermediatebetween that of. the maximum .amplitude -synchrofv nizing` signals andthe'intensity of-'the Whitesignal.

By thev termfmaximum amplitudeV is meant the greatest signal. excursion .from a'lxed referencelevel, that is, from the level of .theiwhitesig- I nals.inzthe. curves;ofiFig.2. Thus, in the .seriesof curves, of Fig. 2a-the vcurve S-represents the maximum v.amplitudeas measured in a positive direction from the level of curve `Wof the white; signal.. Wherean oppositely poled signal is defV rived.;from. .the detector. and Vtranslated through video-frequency: amplifier 22. the synchronizingsignal.. componentswvould.. again designate the maximum. amplitude` from the. reference level, represented. by4 curve W, .but would extend in an opposite direction from. .that reference.

variation from the alternating-current axis.

Referring again tothe series of curves of Fig;

2a, in accordance'with the vforegoing-'definition of a negatively modulated signal, the-black level, represented by curve B,`. represents the maximum amplitude. range of the received carrier-waveY signal .devotedto the transmission of video in formation. This'level extendsfto '75% of the level of V'the maximum carrier-wave amplitude repre-` V sented, byrcurvesA Therefore, the black-levelcorresponds to 1 ai predetermined f fractional por- Viewed.. with respect "to the received .carrier-wave `signal the maximum amplitude is thegreatest signalV 8; tionof-*thwlevel ofjthe=maximumfsigna1 yampli-itudef Theerangerbetweenzthe level of curve1F and theeleveloficurvef-S is allotted tothe-syn chronizing;information;7

Signals; havingn levels of the type described above; asrepresented-bythe/curves of Fig; 2a; are developed across :the network 25, 26, the relative' proportion:offthesignal. across'network 25, 2B' which `is.-deve1opedl across '-resistor 26 being rep-- resented by-lr the series ofV curves of Fig. 2b. Whereas the-'group of 'signals developed across Y resistors 25 fand-*f 26 will occur' having potentials;- which Vare-positive-with respectto a' reference level ofground`orfzero1potential`de to the pointl on Ath'e -network-LMI;Y 25,'126Fat which the anode of tube `22fis connected, they signals. developed across resistor- 2Biwillnormally occur with potentials which Iare-negative with respect to the same ref# erence; level;v Therefore,- theseries of curves of Fig".- Zbrepresent-signal amplitudeswhich are similar to those-of 'the curves of-Fig. 2a but which haverelative amplitudevaluesof one-fourth ofthe latter fsignals iand which occur vwith negative- Ipotentials lwith -respect to ground.

Thesignals= developed across resistor 26 are applied through asignal-translating channel to the-cathode of Arectifier' 33,1 theno-signal level of this lresistorprovidingla -unidirectional bias fpo tential'through resistorf28`=to the-control elec trode of- 'tube 21.

Diode'v 331in combination with theresistor f 28 y' and the condenser 30 is a stabilization device which, in the=absencelofifany fluctuating orvarying'signal appliedto thel'cathode thereof, sta-- bilizes thelsignals-applied to'- its -anode withre spect to the maximum amplitude level of the applied signals; Therefore; if 4the-cathodezof this diode is maintained at a constantpotential of substantially zero-'or-ground-'leveL the group of signals represented bythe curves of Fig; 2a, when translated through condenser' 30 and stabilized by -rectier'-33g= have the: form of theseries of curves'represented-lby Flg=f2c wherein al1' of the applied"signals^are stabilizediwith respect to the maximum signalamplitude. level yas vrepresented by the.- amplitudeiof 'the synchronizing'.v signals. Thus, the synchronizing-signal level, represented by curvev Sinthe seriesfof curves lrepresented by Fig." 2c, isrstabilizedinv such almanner that it is substantially independent 0f the amplitude -variations .of the videoV signals-representedby curves B and W.

If stabilization of the type represented bythe curves. of Fig.' 2c is employed, this being type of stabilizationv present in conventional television as the amplitudes of the-'received video-frequency signals vary.'v Thus; for -every setting of 'the con-'- trast control of a-televisionreceiver and-for every` increase-in the signal intensity of the video sig-I nals,; the-blacl-:'I level ofthe signals changes and' requires readjustmentv in y order" toeffect highU quality reproduction. This Vtype ofarrangement' is considered to belundesirable from` the viewpoint of the 4user-of the television'receiver and the present-invention isparticularly concerned with an arrangement wherebythe signals may be stabilized on` theY black level instead of onn the: synch'ronizingsignallevel.

other-words',` to maintain the'black level sub- -stantially independent of the variations of the average amplitude of the video signal applied to the control electrode of tube 22, rectier 33 is loperated in a manner different from that described above with respect to synchronizingsignal level stabilization. The cathode of tube 33 is not maintained at a constant voltage but varies in accordance with the variation in amplitude of -the series of curves of Fig. 2b. That is, as the nent of the curves of Fig. 2a, the cathode varies from a negative potential in the direction of zero potential in a manner determined by the maximum amplitude of the synchronizing-signal component represented in the series of curves of Fig. 2b. Therefore, the cathode level of rectiiier 33 increases in potential in the same direction as the anode level of this rectier and a predetermined relationshipv is maintained between the relative levels of the anode and the cathode of this tube. This relationship is determined by thev relative signal intensities of the signals developed across the second portion 25, of the network 2d, 25, 2e with respect to the signal intensities of the signals developed across the first portion comprising resistor 25. As has been mentioned above, theseportions bear a relationship to one another of four to one effecting a relationship of variation in signal intensity on the anode of diode'33 which is four times that of the variation in signal .intensity developed on the cathode of this tube.

Since, as has been mentioned previously, in a negatively modulated system, the back signal lever is 75% of the synchronizing signal or maximum amplitude level, the variation in signal amplitude between the back signal level and the synchronizing-signal level is one-fourth of the variation in signal amplitude between the white level and the synchronizing-signal level. Therefore, if a variation of one-fourth of the total signal level is developed on the cathode of rectifier 33 with' respect to lthe variation in signal level developed on the anode of this tube, the synchronizing-signal levelrepresented by curve S of Fig. 2c will be boosted by an amount of 25% thereby producing in the output of the stabilization device 33 a pattern of video-signal components as represented by the series of curves of Fig. 2d' where the black level becomes the stabilized level being substantially independent of the amplitude Variations of other Video-frequency-signal components. When such stabilization is effected, the synchronizing signal represented by the curve S of Fig. 2d will vary in one sense with respect to the stabilized black signal level and the white signal level will vary in an opposite sense.

The signal components translated through the input circuit of tube 21 and stabilized by means of diode 33 with respect to the black level are then directly applied to the control electrode of tube 2l, amplied therein and the amplied signals developed across anode load resistor 3| are applied through terminals 34 and 35 to the image-reproducing unit i l l.

, Having stabilized the video signals so that the black level of these signals is independent of amplitude variations of the Video signal, the operation of the television signal-translating system'is then'similar to the operation of the conventional- Vtelevision receiver 'using V'synchronizing-signal level stabilization. The important difference is that in the presentf'system, when the brightness control of the television receiver vhas been adjusted for properA black level in the conventional manner, any variation in videosignal amplitude, or any adjustment of contrast that'may be lmade, will not affect the initial black-level adjustment.- Thus, with the arrangement described hereinit becomes possible to maintain a constant and proper black jlevel'in the television receiver regardless of variations in the average amplitudeslof signals related to the black level. This desirable feature is'obtained without the need for limiting -the number of video-amplifier stages-that vmay be -used in the television receiver. Itv will be apparent to which the black level' corresponds with '75% of vthe maximum signal amplitude. It is for this reason that the embodiment shows a signal ratio of one to four in the amplitudes ofA the signals applied to the electrodes of diode 33. It will be understood that the invention is not limited to the translation of a video signal in which the black level corresponds to of the maximum carrier-wave amplitude. Where other signal compositions are used, it is only necessary to proportion the described circuit vso that the signal developed` injone portion thereof includes a component that has amplitude Variations which are related to and vary in substantially the same manner with variations inv signal intensity as the level-of a ,selected other signal developed in another portion thereof. Where this operating criterion is satised the combination of such signals provides the desired resultant video signal stabilized on its black level.

While there has beendescribed what is at present considered tobe the preferred embodiment of this invention, it willbe obvious to those skilled in the art that various'changes and modifications may be made" therein without departing from the invention, and itis, therefore, aimed to cover allsuch changes and modications` as fall within the true spiritV and scope of the' invention.

What isclaimed'is:

1. A television receiver signal-translating system for translating a' video-frequency signal having one amplitudelevel representative of synchronizing-signal peaks while apredetermined fractional portion of said llevel is representative of black comprising a source of unidirectional potentials one thereof being positive with respec't to a predetermined reference level andanother thereofbeingleifectively negative with respect to said reference level; a first video-frequency amplifier -for'ft'ranslating Vsaid video-frequency signal comprising an electron-discharge device having a pluraltyof electrodes including an anode and comprising a potential-isolatingv impedance coupledbetween said anode and said positive potential source; a potential-divider network including an intermediate terminal and includingl a pair Vof terminals one of which is coupled to s aidanode and the other to saidI negative potential sourceVthe portion' of said network coupled between said negative potential source and said intermediate terminal having any impedance with relationI to the total impedance of said network as is the amplitude of said synchronzing signal to the overall amplitude of said video-frequency signal; a second video-frequency amplifier includingan input circuit having at least two signal-translating channels one thereof being capacitively coupled to said anode of said rst ampliiier for translating said videofrequency signal developed across said network and the other of said channels being conductively connected to said intermediate terminal for translating the signal developed in said portion and providing a unidirectional potential for said input circuit; and a signal-stabilizing network comprising a peak-rectifying'circuit including a unidirectionally conductive device coupled between said channels and so poled as to conduct upon the application of the peaks of said synchronizing signals thereto and to combine said signals translated in each of said channels, thereby to produce in said input circuit a resultant video-frequency signal having a level representative of said black level and stabilized so that said last-mentioned black level is substantially independent of variations of the average amplitude of said rst-mentioned video-frequency signal. o

2. A television receiver signal-translating system for translating a video-frequency signal having one amplitude level representative of synchronizing-signal peaks while a predetermined fractional portion of said level is representative of black comprising: ak source of unidirectional potentials one thereof being positive with respect to a predetermined reference level and another thereof being effectively negative with respect to said reference level; a iirst video-frequency ampliiier for translating said video-frequency signal comprising an electron-discharge device having a plurality of electrodes including an anode and comprising a potential-isolating impedance coupled between said anode and said positive potential source; a resistor network including an intermediate terminal and including a pair of terminals one of which is coupled to said anode and the other to said negative potential source, the portion of said network coupled between said negative potential source and said intermediate terminal having a resistance with relation to the total resistance of said network as is the'amplitude of said synchronizingsignal to the overall amplitude of said video-frequency signal; a second video-frequency amplifier including an input circuit having at least'two signal-translating channels one thereof being capacitively coupled to said anoderof said first amplier for translating said video-frequency signal developed across said network and the other of said channels being conductively connected t said intermediate terminal for translating the signal developed in said portion and providing a unidirectional potential for said input circuit; and a signal-stabilizing network comprising a peakrectifying circuit including a unidirectionally conductive device coupled between said channels and so poled as to conduct upon the application of the peaks of said synchronizing signals thereto and to combine said signals translated in each of said channels, thereby to produce in said input circuit a resultant video-frequency signal having a level representative of said black level and stabilized so that said last-mentioned black level is substantially independent of variations of the 12 average amplitude oi said'iirst-mentioned videofrequency signal.

3. A television receiver signal-translating system for translating a video-frequency signal having one amplitude level representative of synchronizing-signal peaks while a' predetermined fractional portion of said level isrrepresentative of black comprising: a source-of unidirectional potentials one thereof being positive with'respect to chassis ground level and another thereof being eiectively negative with respect to said ground; a, first video-frequency amplifier for translating said video-frequency signal comprising an electron-discharge device having a plurality of electrodes including an anode and comprising a potential-isolating impedance coupled between said anode and said positive potential source; a potential-divider network including an intermediate terminal and including a pair of terminals one of which is coupled to said anode and the other to said negative potential source, the portion of said network coupled between said negative potential source and said intermediate terminal having an impedance with relation to the total impedance of said network as is the amplitude of said synchronizing signal to the overall amplitude of said video-frequency signal; a second video-frequency amplier including an input circuit having at least two signal-translating channels one thereof being capacitively coupled to said anode of said iirst ampliiier for translating said video-frequency signal developed across said network and the other of said channels being conductively connected to said intermediate terminal for translating the signal developed in said portion and providing a unidirectional potential for said input circuit; and a signal-stabilizing network comprising a peak-rectifying circuit including a unidirectionally conductive device coupled between said channels and so' poled as to conduct upon the application of the peaks of vsaid synchronizing signals thereto and to combine said signals translated in each of said channels, thereby to produce in said input circuit Va resultant video-frequency signal having a, level representative of said black level and stabilized so that said last-mentioned black level is substantially independent of variations of the average amplitude of said first-mentioned video-frequency signal.

4. A television receiver signal-translating system for translating a video-frequency signal havingV one amplitude level representative of synchronizing-signal peaks while a predetermined fractional portion of said level is representative of black comprising: a source of unidirectional potentials one thereof being positive with respect to a predetermined reference level and another thereof being effectively negative with respect to said reference level; a rst video-frequency amplifier for translating said video-frequency signal comprising an electron-discharge-device having a. plurality of electrodes including an anode and comprising a potential-isolating impedance coupled between said anode and said positive potential source; a potential-divider network including an intermediate terminal and including a pair of terminals one of'which is coupled to said anode and the other to said "negative potential source, the portion of said network coupled between said negative potential source and said intermediate terminal having an impedance which is one-quarter of the total impedance of said network as is the amplitude vof said synchronizing signal one-quarterof the overallamplitude of said video-frequency signal; a second video-frequency amplier including an input circuit having at least two signal-translating channels one thereof being capacitively coupled to said anode of said first amplier for translating said video-frequency signal developed across said network and the other of said channels being conductively connected to said intermediate terminal for translating the signal developed in said portion and providing a unidirectional potential for said input circuit; and a signal-stabilizing network comprising a peak-rectifying circuit including a unidirectionally conductive device coupled between said channels and so poled as to conduct upon the application of the peaks cf said synchronizing signals thereto and to combine said signals translated in each of said channels, thereby to produce in said input circuit a resultant video-frequency signal having a level representative of said black level and stabilized so that said last-mentioned black level is substantially independent of variations of the average amplitude of said rst-mentioned video-frequency signal.

5. A television receiver signal-translating system for translating a video-frequency signal having one amplitude level representative of synchronizing-signal peaks while a predetermined fractional portion of said level is representative of black comprising: a source oi unidirectional potentials one thereof being positive with respect to a predetermined reference level and another thereof being eifectively negative with respect to said reference level; a rst video-frequency amplifier for translating said video-frequency signal comprising an electron-discharge device having a plurality of electrodes including an anode and comprising a potential-isolating impedance coupled between said anode and said positive potential source; a potential-divider network including an intermediate terminal and including a pair of terminals one of which is coupled to said anode and the other to said negative potential source, the portion of said network coupled between said negative potential source and said intermediate terminal having an impedance with relation to the total impedance of said network as is the amplitude of said synchronizing signal to the overall amplitude of said video-frequency signal; a second video-frequency amplifier including an input circuit having at least two signal-translating channels one thereof being capacitively coupled to said anode of said rst amplifier for translating said video-frequency signal developed across said network and the other of said channels being conductively connected to said intermediate terminal for translating the signal developed in said portion and providing a unidirectional bias potential with respect to said predetermined level for said input circuit; and a signal-stabilizing network comprising a peak-rectifying circuit including a diode having the anode thereof coupled to said one channel and the cathode coupled to said interu mediate terminal thus being so poled as to conduct upon the application of the peaks of said synchronizing signals to said anode of said diode and to combine said signals translated in each of said channels, thereby to produce in said input circuit a resultant video-frequency signal having a level representative of said black level and stabilized so that said last-mentioned black level is substantially independent of variations of the average amplitude of said first-mentioned videofrequency signal.

WILLIAM F. BAILEY.-

REFERENCES CITED The following references are of reccrdin the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,240,281 Ballard Apr. 29, 1941 2,259,520 Freeman Oct. 21, 1941 2,463,735 Bedford Mar. 8, 1949 FOREIGN PATENTS Number Country Date 515,426 Great Britain Dec. 5, 1939 

